Excessive confidence in visually-based estimates

People exhibit excessive confidence in visually-based estimates, which in turn biases decision making. Three experiments support this assertion. Experiment 1 shows a strong impact of presentation format on estimation of proportions. Experiment 2 shows that people rely on these erroneous estimates to make incentive-compatible decisions even when objective information can be easily obtained. Experiment 3 demonstrates that the biased decisions disappear when confidence in visually-based estimates is called into question by the perceived complexity of the stimulus.